Comparative structural analysis of the MOMP isolated from different Chlamydia trachomatics strains is being done using two different peptide mapping techniques. MOMPs isolated from either 14C-intrinsically radiolabeled chlamydiae or lactoperoxidase madiated surface-radioiodinated organisms were digested with Staphylococcus aureus V8 protease and the peptide fragments produced displayed by SDS-PAGE or they were digested with alpha-chymotrypsin nd the peptides analyzed following separation by high-voltage electrophoresis and thin-layer chromatography. The results show that considerable structural homology exists among different C. trachomatis MOMPs, however, distinct differences in primary structure were found. These differences were most obvious in peptide maps of MOMPs isolated from surface-iodinated organisms suggesting that the exposed portions of the MOMP may differ antigenically and are possibly the determinants that elicit the formation of C. trachomatis serotyping antibodies. Currently, the surface peptide fragments identified by mapping analysis are being isolated by high-pressure liquid chromatography. Antisera will be raised against these isolated peptides in order to define their immunological properties.